Electric pulse modulator



March 1953 T. H. FLOWERS 2,632,880

- ELECTRIC PULSE-MODULATOR Filed Feb. 26, 1951 2 SHEETS-SHEET l K A -vgl "V3 [119:2 "WEN-role, 7750/7740 /7. Howe/1s ATT0RNEY Patented Mar. 24, 1953 Thomas Harold Flowers, London, England:

Application February 26, 1951, 'SerialNo. 2125736 In Great Britain March 3; 1950- {Ha-inns. (01. 332-11 li'liis:invention relatesto electric pulse modul'ators whichplace-cyclically and in order a-:pluralityof electrical! communication: channels in communication with" a common multiplex" channel." One of'the object's ofthe invention is to reduce-the number of; and to simplify the pulse sources which maybe. provided forsuch multiplex pulse-modulators to modulate a given number of channels;

According 'to 'th'e present invention in an nchannel m-ultiplex pulse-modulator the number n is-the-product of at least two integers which are prime" to one another and the modulator comprises-aplurality of groups of sources of pulses, onegroup for each of the integers; the number of sources of pulses in each group being equal to the value of" 'theinteger which the group represents, each pulse source having a pulse repetiti'on-frequency inversely proportional to the integerof thegroup of which the pulse source forms part", the trains of pulses of each group of pulse sources-being timesp'aced at equal intervals within the pulse repetition period of the group and the pulses in the d ifierent' groups being synchronised.- so' that when 'a'pulse occursin one group a pulse occurssimulta-neously in all the groups.

a particular application of the invention a multiplex pulse modulator comprises a plurality of stages of modulation; each stage except the last com-prising. at least two-equal-sized groups of modu1ators--each group of which is connected in tandem with a modulator of the next stage, While-thelast stage comprises a group of modula'tors connected to a common channel, the numher of modulators in the groups in the several stagesare prime to one another, a plurality of groupsof' sources of pulses are provided one group for-each stage of the multiplex modulator, agroup of sources ofpulsescomprising a plurality of pulse sources each connected to one modulator in each group-oi a stage and having a pulse repeti'tion frequency inversely proportional to the numberof modulatorsin the group, the trains ofpulses of 'eaeh" group of pulse-sourcesqbeing time-spaced at equal intervals within the pulse repetition periodof the g1'oup=-and-;the pulses synchronised-to that when a pulse occurs in one group of pulses apulse occurs simultaneously in all the groups-of pulses. V

In aiurtherapplicaticn of the invention an n-channel multiplex pulse modulator comprises 'n modulators for: placingn channels in electrical communication inturnwith a common channel; thenumber n? beingithe product 'of' at leasttwo integers which'are prime to one another, a plu pulse source havinga pulserepetition frequency inversely" proportional to the integer of the'group of which the pulse source? forms part, the: trains of' pulses of each. group" of pulse sources being time-spaced at equal intervals within-the pulse repetition" period oitheegroup and the pulses being" synchronised so: that'whena pulse occurs in one group a pulse occurs simultaneously in all the groups, and, each modulatcris: connected to a unique combination of pulse sources comprising'one' pulse source-in eachgroupcof; pulse sources, and places: itsvchannel in electrical communication with the: common channel on the simultaneous occurrence of a pulse: from each of the pulse, sources to which it 'is connected;

In order that the inventionmay be moreiclearly understood andireadilycarried into: effect, alter= nativeapplicationsthereof will now be described in greater detail byway of example; with" refer= ence to the accompanyingdrawings in WhlCl'H- Fig; I shows one fornrof'pulse groups suitable for use in carrying out 'the' invention;

Fig. 2' is a part" of 'a" circuit for generating :such pulse groups" given by way of example and not forming partof the present invention and:

Figs. 3 andf l are p'artial' circuit arrangements of alternative modulating arrangements embody-- ing the invention;

Referring. to' Fig. 1,; twogroups of "sets of 'pulses; which for' convenience will be referred to as pulse sources as used in carrying out the invention are illustrated; one roup along linesal to al l and the other group along lines hi to bill. One group comprises eleven and the other ten pulse sources which numbers are prime to one another; The pulse sources are suitable, aswill be explained hereafter; for a llflj-channel multiplex pulse. modulator, the number being the product of the. twov numbers 11 and 10; The pulserepetition frequency of the pulses all. to a! l is 10/11 where for is a suitable base frequency and the trains of pulses from each source are time-spaced order at intervals of l/fo, if e; the period" of the basefrequency, and-are thus equallytime-space'd within the pulse repetition period. The-pulse repetitirinirequency of; the pulses" bl; to: brllvis: fo/lwwhere fo' is thevsame base frequency as that of the pulses al to all, and the trains of' 'puls'es from: each source are time spaced inorder at intervals' of" I/fwi. e.

the same time spacing as the pulses a! to a! I. The pulses from the two groups are synchronised so that when a pulse occurs in one group a pulse occurs simultaneously in the other group. The widths of the pulses may be any suitable value up to the value of the time-spacing of the pulses i. e. up to l/fo.

Circuit arrangements or devices providing groups of pulses as illustrated in Fig. 1 may take any convenient form, but one arrangement which may be used with advantage although as previously stated, not forming part of the present invention per se, will be described with reference to Fig. 2.

Referring to Fig. 2, valve VI is part of a blocking oscillator pulse generator which, when suitably controlled, generates a voltage pulse across resistor I I connected between the cathode of the valve VI and earth, which voltage is shown in the diagram as applied to a coaxial pulse lead The anode of valve VI is connected via the primary winding of a transformer I2 to a suitable potential +V2 positive with respect to earth potential. The control grid of valveVI is connected through the secondary winding of trans-- former I2 in series with the parallel combination of a resistor I3, an electrical delay line I4 and a condenser I to a source of negative potential -VI of value sufilcient and preferably slightly more than just sufficient when applied to the control grid, to cut-01f the anode current of the valve VI. The delay line I4 is open-circuited at its end remote from the resistor- I3 and condenser I5 and has a delay time equal to half the duration of the pulse which the pulse generator is required to generate. Let it be supposed that the circuit so far described has reached steady state condition with the valve VI in the anode current cut-off state. Then it is well known that if anode current is started by some external means,

it is augmented by the feed-back to the control grid of the potential of which rapidly becomes such that grid current flows and a large total cathode current is caused to flow. This cathode current produces a positive voltage across the impedances in the cathode circuit. The grid current produces a steep-fronted voltage rise into the delay line I 4. Reflection of the voltage at the open-end of the delay line causes a negative voltage to be applied to the control grid of valve VI through the secondary winding of transformer I2 at a time equal to twice the delay time of the delay line after the initial rise of current in the valve. The negative voltage is again augmented by the feed-back to the control grid and the valve VI rapidly returns to the anode cutoff condition, thus completing the generation of a pulse in its cathode circuit. The valve is then blocked against further operation until the energy in the magnetic circuit of the transformer I2, the capacitor I5 and delay line I4 have been substantially dissipated.

In the case of a pulse group generator for use in carrying out the present invention, blocking oscillator pulse generators equal in number to the number of pulses in the group may be provided and operated in order from a source of pulses of the required base frequency connected to lead KI. In Fig. 2 a second blocking oscillator pulse generator is shown comprising valve V2, and components similar to those associated with valve VI are similarly designated except that the first numeral of each designation is 2 instead of l. The operation of each blocking oscillator pulse generator in turn from the base frequency pulses,

4 which for convenience will be designated KI will now be described.

The anode of valve VI is connected to the anode of a valve VII of which the anode current is normally cut-off. Let it be supposed that the valve VII is caused to conduct by a KI pulse. The transformer I2 causes the anode current in valve VII to produce a positive voltage to be applied to the control grid of valve VI, which then conducts on its anode circuit. A positive pulse is then produced in the cathode circuit and communicated to the lead pl and a negative pulse is produced in the anode circuit of valve VI as already described. The negative pulse at the anode of valve VI is caused to prepare the operation of the blocking oscillator comprising valve V2 in response to the KI pulse following the KI pulse which caused the operation of the blocking oscillator comprising valve VI, as will now be described.

Valve V2I has its anode connected to the anode of valve V2 and its cathode connected to earth. Its anode current is normally cut off as will be clear later and when made to fiow causes the blocking oscillator comprising valve V2 to generate a pulse over lead 112 in a similar manner to that described for the generation of a pulse over lead pI in response to anode current flow in valve VII. The KI pulses have an amplitude approximately equal to the grid base of valve V2I and are communicated to the control grid via condenser C2I. The mean value of the control grid potential is, however, controlled so that in the steady state, the control grid potential is never positive enough to cause anode current to flow. The mean value of the grid potential in the steady state is substantially that of the negative bias potential V3 which is applied via the parallel connected resistor 25 and rectifier 26 in series with resistor 21 to the control grid. The junction of the resistors 25 and 21 is connected via resistor 28 and condenser C22 to the anode of valve VI.

When a negative-going pulse is produced at the anode of valve VI as already described, the condenser C22 charges during the negative excursion of the anode voltage so that its plate connected to the anode is negative with respect to its other plate. The charging is assisted by the rectifier 26 which effectively short-circuits the resistor 25 at this time. When the anode voltage returns to normal at the end of the pulse, the charge on condenser C22 is discharged through resistor 28 and raises the potential of the junction of resistors 28, 21 and 25 to the potential V2 at which it is clamped by the rectifier 29. Potential V2 is approximately the control grid potential of valve V2 I at which anode current cut-off occurs. This potential is applied via resistor 21 to the control grid and when a KI pulse via condenser C2I is superimposed on this potential, the valve V2I conducts and causes the blocking oscillator pulse generator comprising V2 to generate a pplse similarly to that previously described for the blocking oscillator comprising valve VI. It was assumed that a KI pulse caused the valve VII to conduct and it has been described how when valve VI I is caused to conduct, pulses are generated at the cathode and anode of valve VI and at the conclusion of the pulses the control grid potential of Valve V2I is raised to a value at which a superimposed KI pulse will cause that valve to conduct.

The duration of the KI pulses is arranged to be less than that of the pulses generated by the assassin hlockingzoscillatorsa Hence; whenith'eidischarge ofiscondensericfl -rai'ses the controli'gridzpoten: tialzL on the-:1 valya- VZL'. its, does; sow; after: the; K I pulsez which operatedzvalyezvsltk:hasmeased. The capacitance.ofiithehcondenser"C22 and the-icon;- stants; of; the :anetworkr comprising. resistors: 23; 2:5 andipotential ;holding:rectifier 2-9 are. chosen SOP-217119.12 tatheridischarge of condenser C22 xraises therpctential ot the"; control grid of." valveaVZl ion-a period longt-enoughr-fonthat valve: to;-.=be rendercrhoonductingrbya1;leastsone Ki: pulse following-the 1 pulsez which; renderedj, valve lZ-trhconductihgzrbut preferably" for not more than:.-one 101:: :two: such :.K Li pulses; A. pulsexthus prcdwced. verileadfrpl in: responsato-xoneeKi pulsenwill; thus. e1 .followed-flaya pulse 1 oyer lead p2: imnespnnse to"; theznextipK I. pulse'aandi itegwill hosavapparent that; further: blockingr oscillator pulse-r,-generatorsr chain: connection following thatrcomprising: valve V2: will. generate pulses in response to successive Kl pulses: If. valve W243; for? example;v is: caused. to COIldllClJTTbY two successive K I pulses; onlytheifirst' will. be sucrcessf'ulsirr pulsing .valve V'ZJbecauseofithe blocked period which; follows the: generation; o'f'a pulse:

Lietriti'be assumed that :the chain of" blocking oscillators isclosedsin: a. ring and; that one: of thenr is: caused to be operated by a K 1 pulse; theme will? be apparent that the blocking oscil lators white and provid' at: thexring contains the appropri-ate number-of blocking oscillators. the pulses produced ontheir 13 leadswill be a group: of pulses as shown' in Figure I, for the group a! t'o=-a;l l or b] to b'lfl' a" It" is'necessary, however, that the pulse generation best-arted for example bycausing-valve VH to conduct; This is ac compli'shed by-opcra-ting-the key K to open its contact and thus to raise the mean potential of the control grid of Va'IVEVI I to the potential -V2-and permitting'Klpulsesto operate that valve; 1 The bIockingoscillator comprising valve VI will then generate pulses spaced apart; by the. blocked time of the oscillator; and these will circulatero'und' thering' as previously described; andmcre than one pulse willbe caused'to" start circulating.

The continuedcirculation ofmorethan one pulse. round .the ring. may. be prevented. by. arrangingthe blocked time after the generation oiapul'se by abl'ocking. oscillator to exceed half the. periodof the. ring. cycle of. operationsyallthough. the time .must... of course. be less. than said period The. blocked. time. .may be. con: trolled by condenser, for. example. condenser for theblo cking; oscillator. comprising valve VI.v

Itswill. be. seen that it a v plurality of, rings; of blocking. oscillators as. described. are. provided each. with anv appropriate number of blocking oscillators. in; thearing and; all the. rings. arev driven-from: the same Kt pulsesource... groups of pulses: as. required; inacarrying. out the. presentr-invention and as-illustrated by way of example in Fig. 1 may be produced.

A particulanapplication of the'invention to a.v 110-channel -2-stage. multiplex modulator. is illustrated in Fig. 3. The modulatorsillustrated are fully described in the specification of 00- pending patent application S; No. 191,584 filed October'23, 1950 by Thomas Harold Flowers: and John Edward Flood and. are: therefore. only briefly described in this specification.

The 110-channels are divided into ten groups each of eleven channels and each channel is eratedfimorder by'the Kl pulses connected in turn to the common yl.

each of: elevenmodulatorsaare. provided... For.

the-sake of clearness. o'fthe. figurexonly six: chamnels and their: first stage modulators: are; shown. Channel's I :c'|',. lxZ; lwll are the. first; second and eleventh channelsof the: first group; and channels 2x1, 2x2: and. 2.17M the first; second and eleventh. channelssof the'second group.l The remaining channels not shown will be readilyappreciated. Allthe modulators arer similarand only that connected to channel Ix]: will be--de-. scribed-indetail. The modulator comprises. two rectifiers WI and W2. in. series and of theisame polarity in the serie connctiom The. channel lml is'connected to'the junction ofthetwo rectifiers, the other side of rectifier WI 'is-connecte edl'to earth and the other side of rectifi'er'W2 toa group channel y!. The junction of the two rectifiers is" supplied with bias current" via a resistor SE! from all C; potential -Vnega'- tive with respect to earth and pulse current via a resistor 3R2 from a pulsesource al. The-pulse source al is one of eleven-sources, al, a2,

all as described and illustrated with reference to Fig; 1. The bias and pulse currents are arranged so that in the absence of a pulse from source al current flows through rectifierWfin its low' resistance direction of conduction but in the presence of azpulse current flows through rectifier W2 in its low resistance direction of conduction and connects the. channel [ml to the common 21!. Each modulatorin group I is connected to a different. one of the pulse sources a! to all. Henceeach channel Ix] to lxll is Similarly each channel 230! to 23st! is connected in turn to the common g2 and so on for each of. the ten groups. A pulse in any one of the pulse sources a! to all thus connects one channel in each group to a common y channel, and the second stage of modulation connects one of the channels. to thecommon multiplex channel. ,2 as. will now be explained.

The common. y. channel. of each first. group of modulators is connectedthrough a second. stage modulator to. the commonmultiplex channel a. A second stage modulator is similar to the first stage modulators in that it comprises two rectifiers, 3W3 and. 3W4 in the case ofv the common channel yl. and 3W5 and 3W6 in. the case of the common channel 112, a source of D. C. bias -V andv a pulse source e. g. b1, b2, andthe series rectifier conducts in its low resistance direction only in thepresence of an impulse from the pulse source. Thepulse sources bl to bl 0 are provided as descrihedand illustrated withre'ference to Fig. 1 and the ten: second. stage mod..- ulators are connected one to'each ofthe pulse sources. It is thus apparent that although a pulse from one of the sources-a! tooll-connects one channel in each first stage group to a common yrchannel only that channel which is: connected to the y'common which is simultaneously connected to the a common channel by a pulse from: a source bi to bs 'will'be connected to the 2 channel. It will befurther apparent that each of the -channels will be connected in turn incyclic order to-the multiplex channel because the number of channels in the first stage groups is prime to the number of channels in the second stage.

In the further application of the invention shown in Fig. 4 110 channels are multiplexed to a common channel in one stage of 110 mod ulators, of which two only are shown in the figure. The modulators are all similar and only one will be described. Each comprises two rectifiers WI and W2 in series connection and the same polarity in the series connection. The channel, he! in this case, is connected to the junction of the two rectifiers, the other side of rectifier WI is connected to earth and the other side of rectifier W2 is connected to the common multiplex channel '2. The rectifiers are biased from three sources, through a resistor QRI from a potential +V positive with respect to earth through a resistor 6R2 and rectifier W3 in series from a potential V negative with respect to earth and, through a resistor 4R3 and rectifier W4 in series from the potential V. The bias currents are arranged so that current from source --V through either or both rectifiers W3 or W6 produces current through rectifier VJ! in its low resistance direction of conduction, but with current through neither rectifier W3 nor W4,'bias current from source l-V produces current through rectifier W2 in its low resistance direction of conduction and connects the channel lrcl to the common multiplex channel .2.

Pulse sources al to all and bi to bill are provided as described and illustrated with reference to Fig. 1 except that in this example negative pulses are required from the pulse sources. The polarities of the pulses shown in Fig. 1 may be reversed by transformers. The junction of resistor 4R2 and rectifier W3 is connected via a condenser CI to one of the pulse sources in the al to all group, connection to a! being shown in the drawing. The junction of resistor 3B3 and rectifier W is connected via a condenser C2 to one of the pulse sources in the bi to bill group, connection to bl being shown in the drawing. The amplitude of a pulse from source al is arranged to be such that rectifier W3 is rendered a high-resistance, and similarly a pulse from source bl renders rectifier W4 a high-resistance. From the previously described conditions for connection of the channel is! to the channel 2 it will be seen that this connection occurs only on the simultaneous occurrence of a pulse from the sources a! and bi. It will be further apparent because of the prime number relationship between the number of pulse sources in the two groups of pulse sources, by connecting eachof the 110 modulators to a different combination of one pulse source in each group of pulse sources, each of the 110 channels may be connected in cyclic order to the common multiplex channel.

Examples have been described of IlO-channels modulators which may be operated from 21 pulse sources in two groups one of eleven and the other of ten derived in simple manner from a common base frequency. Other arrangements will be apparent; for example, fifteen sources of pulses in three groups of seven five and three pulse sources respectively may be provided for a IDS-channel multiplex in three stages in series, or in one stage using combinations of the pulses, or in two stages in series one of the stages using combinations of pulses from two of the groups of pulses.

I claim:

1. A multiplex pulse modulator comprising a plurality of stages of modulation, each stage except the last comprising at least two equalcommon multiplex sizedgroups of modulators each group of which is connected in tandem with a modulator of the next stage, while the last stage comprises a group of modulators connected to a common channel, the number of modulators in the groups in the several stages being prime to one another, a plurality of groups of sources of pulses, one group of said plurality of groups being provided for each stage of the multiplex modulator, a group of sources of pulses comprising a lurality of pulse sources each connected to one modulator in each group of a stage and having a pulse repetition frequency inversely proportioned to the number of modulators in the stage, the trains of pulses of each group of pulse sources being time-spaced at equal intervals within the pulse repetition period of the group and the pulses synchronised so that when a pulse occurs in one group of pulses a pulse occurs simultaneously in all the groups of pulses.

2. A multi-channel multiplex modulator comprising in combination 1!. channels, n being the product of at least two integers which are prime to one another, 11 pulse modulators each of which is connected to one of said channels, groups of pulse sources, one group for each of said integers, the number of pulse sources in each group being equal to the value of the integer which the group represents, each pulse source having a pulse repetition rate inversely proportional to the integer represented by the group of which the pulse source forms part, the trains of pulses of each group of pulse sources being time spaced at equal intervals within the pulse repetition period of the group and the pulses in different groups being synchronised so that when a pulse occurs in one group a pulse occurs simultaneously in all the groups.

3. A multi-channel pulse modulator comprising in combination n channels, n being the product of at least two integers which are prime to one another, 12 modulators each of which is connected to one of said channels, a common channel to which said modulators are connected, a plurality of groups of pulse sources, one group for each of said integers, each group containing a number of pulse sources equal to the value of the integer which the group represents, each pulse source having a pulse repetition frequency inversely proportional to the integer of the group of which the pulse source forms part, the trains of pulses from each group of pulse sources being time-spaced at equal intervals within the pulse repetition period of the group and the pulses being synchronised so that when a pulse occurs in one group apulse occurs simultaneously in all the groups, each modulator being connected to a unique combination of pulse sources comprising one pulse source in each group of pulse sources and which places its channel in electrical communication with the common channel on the simultaneous occurrence of a pulse from each of the pulse sources to which it is connected.

THOMAS HAROLD FLOWERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,556,200 Lesti June 12, 1951 

